US3714424A - Apparatus for improving the signal information in the examination of samples by scanning electron microscopy or electron probe microanalysis - Google Patents

Apparatus for improving the signal information in the examination of samples by scanning electron microscopy or electron probe microanalysis Download PDF

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Publication number
US3714424A
US3714424A US00122785A US3714424DA US3714424A US 3714424 A US3714424 A US 3714424A US 00122785 A US00122785 A US 00122785A US 3714424D A US3714424D A US 3714424DA US 3714424 A US3714424 A US 3714424A
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United States
Prior art keywords
sample
image signal
improvement
electrons
modulating means
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Expired - Lifetime
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US00122785A
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English (en)
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U Weber
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Siemens AG
Siemens Corp
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Siemens Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/252—Tubes for spot-analysing by electron or ion beams; Microanalysers
    • H01J37/256—Tubes for spot-analysing by electron or ion beams; Microanalysers using scanning beams
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/244—Detectors; Associated components or circuits therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
    • H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/244—Detection characterized by the detecting means
    • H01J2237/2448—Secondary particle detectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/244—Detection characterized by the detecting means
    • H01J2237/2449—Detector devices with moving charges in electric or magnetic fields
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/244—Detection characterized by the detecting means
    • H01J2237/24495—Signal processing, e.g. mixing of two or more signals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/245—Detection characterised by the variable being measured
    • H01J2237/24507—Intensity, dose or other characteristics of particle beams or electromagnetic radiation

Definitions

  • This invention relates to an apparatus associated with the scanning electron microscopy and the electron probe microanalysis wherein the surface of a sample face is scanned by means of a primary electron beam, and the electrons emitted upon bombardment with the primary electron beam are sensed by means of a secondary electron detector.
  • the outer configuration (topography) of a sample may be analyzed, while with the aid of an electron probe microanalyzer an elementary analysis of the sample surface may be performed.
  • the results of these analyses may be plotted by means of an evaluating device or may be represented as an image. In both analyzing devices it is a requirement to detect with great sensitivity even very small structural differences in a sample face and to furnish contrast-rich images with optimal resolution.
  • a magnetic deflecting system is incorporated in the electro-optical system of the electron gun.
  • the magnetic deflecting system permits by means of linewise deflection of the primary electron beam over the sample face and by means of synchronously controlled evaluating devices (registering devices, data supply devices, plotters, image forming apparatus, etc.) the measuring and representation of the course of signal intensity along lines or over a range of the sample face.
  • evaluating devices registering devices, data supply devices, plotters, image forming apparatus, etc.
  • a dot analysis of the sample can also be performed.
  • the surface structure ofa sample is to be examined by means of either one of the afore-outlined analyzers, it is sought to utilize for the image formation only 'the low-energy secondary electrons emitted by the sample as a result of its bombardment with the primary electron beam, while the backscattered electrons should not be used.
  • the reason therefor is that the dot resolution in the analysis of a surface of a sample having a large mass is by one order of magnitude better when performed with the aid of secondary electrons than if backscattered electrons are used.
  • scanning electron microscopes which, for the purpose of an electro-optical representation of microstructures of a sample face at extreme magnification and resolution, scan the surface with an extremely thin primary electron beam in a linewise manner for the image formation, utilize, among others, a so-called secondary electron detector.
  • the latter indicates the detection of secondary electrons, emitted by the sample surface, by means of an amplified current signal which is a function of their number.
  • a secondary electron detector of this type comprises an electro-optical system and an indicating system.
  • the electro-optical system has the function to deliver to the detector as many secondary electrons as possible as they leave in all directions the locus of impingement of the primary electron beam on the sample face.
  • the indicating system the relatively slow secondary electrons are first applied to a post-accelerator system which accelerates them to an energy sufficiently high (approximately l-l 5 keV) for increasing the sensitivity of indication.
  • the accelerated electrons enter an electron multiplier or a scintillation crystal after which there is connected a sensitive photomultiplier or a semiconductor detector.
  • a secondary electron detector necessarily responds also to the rapid backscattered electrons which are emitted from a larger surrounding area of the locus of impingement of the primary electron beam on the sample face.
  • the signal of the backscattered electrons limits the image resolution and causes the image contrast to deteriorate. If the sensitivity of indicating backscattered electrons by the secondary electron detector is decreased, then a loss of sensitivity with respect to the secondary electrons has also to be taken into account.
  • Tertiary electrons are secondary electrons which are emitted by adjacent components (such as the pole piece of the electron lens assembly, or the walls of the sample chamber) upon bombardment by the backscattered electrons.
  • adjacent components such as the pole piece of the electron lens assembly, or the walls of the sample chamber
  • the image signal formed by the parasite electrons may be stronger than the image signal of the secondary electrons.
  • an image signal emitter which is tuned to the frequency of the modulating apparatus and which is connected after the secondary electron detector.
  • FIG. 1 is a schematic representation, including a circuit diagram, of a first embodiment of the invention.
  • FIG. 2 is a schematic representation, including a circuit diagram, of a second embodiment of the invention.
  • a primary electron beam E passes through an electron lense L and is deflected to scan a sample P.
  • the electronic deflecting apparatus including an associated control system is of conventional nature and is not illustrated.
  • the sample I and the electron lense L are surrounded by a sample chamber wall W.
  • the normal of the sample face is moved from its position parallel to the primary electron beam E through an adjustable angle a in the direction of a secondary electron detector D known by itself.
  • the first output terminal XI of an oscillator is connected with the sample P, whereas the second output terminal K2 is connected with the sample chamber wall W. Both the sample chamber wall W and the electron lense L are grounded (i.e. they are at zero potential).
  • the oscillator O delivers an alternating voltage of a frequencyfand generates an alternating electric field in the order of V/cm in a condenser, one electrode of which is formed by the sample P, while the other electrode of which is formed by a component adjacent the sample P, such as the sample chamber W and the electron lense L.
  • the second output terminal K2 of the oscillator 0 instead of connecting it to components W and L may be connected to an auxiliary electrode disposed in the space in front of the sample face.
  • the auxiliary electrode may be an annular disc or may have a pointed, or edge-like or sieve-like configuration.
  • the secondary electron detector D applies to the input terminals El and E2 of an image signal emitter such as a phase-responsive rectifier (lock-in amplifier) PG, a voltage which is proportionate to the number of electrons entering its inlet opening F.
  • the input terminal E2 is grounded.
  • additional input terminals L1 and L2 of the phase-responsive rectifier PG are connected with the output terminals KI and K2 of the oscillator 0 through a potentiometer RI.
  • the phase-responsive rectifier PG preferably contains a phase adjusting component.
  • the image signal S delivered by the phase-responsive rectifier PG is applied to a known evaluating apparatus A, such as an image forming device controlled synchronously with the scanning motion of the primary electron beam E.
  • a direct electric field of a magnitude in the order of I00 L000 V/cm there is generated a direct electric field ofa magnitude in the order of I00 L000 V/cm.
  • a voltage source B1 of approximately 200 V is connected between the inlet opening F of the secondary electron detector D and the components adjacent the sample P.
  • the positive pole of the voltage source B1 is applied to the inlet opening F, whereas its negative pole is grounded. It is to be understood that for some purposes a reversal of the poles may be expedient.
  • the purpose of this electric field is to securely discriminate between the electrons entering the detector opening F and to obtain at the output of the secondary detector D an as large an output signal as possible.
  • a further electric DC field of adjustable magnitude and direction may be generated at the sample face.
  • the center tap of a further potentiometer R2 which is connected to a further voltage source B2, is connected with the sample P.
  • a reversing switch U is provided to reverse the polarity of the potential applied to the sample P.
  • One pole of the voltage source Bl is always grounded.
  • the sample P is at a negative potential (for example 5 V) with respect to its environment (W, L).
  • the direction of this electric field is set by adjusting the angle 0: and/or by actuating the reversing switch U,
  • the high-energy (for example, 20 keV) beam E of the primary electrons causes, at the bombarded location of the sample face, an emission of high-energy (approximately 20 keV) backscattered electrons e,., lowenergy (approximately up to 50 eV) secondary electrons e, and also, in a smaller number, low-energy Auger-electrons (not shown).
  • high-energy for example, 20 keV
  • lowenergy approximately up to 50 eV
  • Auger-electrons not shown.
  • FIG. 1 conditions are shown at a moment when the negative amplitude (for example -10 V) of the alternating voltage supplied by the oscillator O is applied to the sample P, the potential of which is then l5 V with respect to the ground.
  • the backscattered electrons e emitted by the sample face leave the latter in linear paths since, due to their high kinetic energy, they are unaffected by the momentarily positive potential (in the example a total of 215 V) of the detector opening F.
  • a small portion of the backscaattered electrons e enters the detector D.
  • the low-energy secondary electrons e are deflected along curved paths in the direction of the detector opening F.
  • Some of the low-energy tertiary electrons e emitted by adjacent components (such as the electron lense L or the wall W of the sample chamber) upon their bombardment by the backseattered electrons 2, also enter the detector opening F.
  • a positive amplitude for example l0 V
  • the potential of the sample P is +5 V with respect to the ground.
  • the rapid backscattered electrons e,- are, as before, unaffected by the potential (now I V) applied to the detector opening F.
  • a small portion of the back-scattered electrons e enters the detector D.
  • the tertiary electrons e because they are generated by the backscattered electrons e,., are little affected by the change of potential of the sample P.
  • the periodic variation of the electric field between sample P and the adjacent components affects mostly the secondary electrons e,: they are periodically and in an alternating manner withheld or accelerated.
  • the phase responsive rectifier PG only that component of the output voltage of the secondary electron detector D is amplified and rectified which varies periodically and in phase with the frequencyfof the oscillator O.
  • the image signal S thus contains mostly that information pertaining to the structure of the sample face which is carried by the secondary electrons e,.
  • the current of low-energy electrons entering the secondary electron detector D is weakened periodically by means of an alternating magnetic field having a magnitude between 1 and 100 oersteds.
  • a narrow bandpass filter F which is tuned to the frequencyfof the oscillator O and after which there is connected an amplifier V.
  • the output signal of the latter is applied, as an image signal S, to an evaluating device A and is plotted synchronously with the scanning motion of the primary electron beam E. It is noted that the fields should be so directed and their intensity so chosen that they have negligible or no effect on the primary electron beam.
  • the advantages achieved by means of the invention reside particularly in the fact that in forming the image of a sample surface optimal resolution and extremely differentiated image contrast may be achieved since exclusively electrons of low energy, mostly secondary electrons, take part in the image formation. Furthermore, contrary to the conventionally used secondary electron detectors, an energy analyzer is no longer necessary for keeping the backscattered electrons away from the detector. Such a measure has led to a loss of sensitivity. Further, by practicing the invention, the detector opening F no longer has to be brought into a geometrical position to render impossible the entry of backscattered electrons. Instead, the secondary electron detector may be oriented towards the sample in the immediate vicinity thereof even if the sample face is normal (or to the bombarding primary electron beam. In the latter case an alternating electric field of high amplitude may be generated at the sample face even with a low alternating voltage. During the half period when the negative amplitude is applied to the sample, there results an increase in the number of secondary electrons that reach the detector.
  • an apparatus for analyzing a sample said apparatus being of the type that includes a secondary electron detector having an inlet opening receiving high-energy and low-energy electrons emitted from a face of said sample upon bombardment with a scanning primary electron beam, the improvement comprisirfig Id modulating means generating an alternating at said sample face for effecting, with a determined frequency, a periodic decrease solely of the current of said low-energy electrons entering the inlet opening of said secondary electron detector; the possible range of said periodic decrease includes an interruption of said current and B. an image signal emitter connected to said secondary electron detector to receive the output signals of the latter, said image signal emitter being coupled to said modulating means for tuning said image signal emitter to the frequency of said modulating means.
  • said modulating means includes means for generating an alternating electric field at the sample face from which said electrons are emitted.
  • said modulating means includes means for generating an alternating magnetic field at the sample face from which said electrons are emitted.
  • said image signal emitter includes A. an amplifier and B. a narrow bandpass filter connected to and before said amplifier and tuned to the frequency of said modulating means.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
US00122785A 1970-03-10 1971-03-10 Apparatus for improving the signal information in the examination of samples by scanning electron microscopy or electron probe microanalysis Expired - Lifetime US3714424A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2011193A DE2011193C3 (de) 1970-03-10 1970-03-10 Vorrichtung für die Elektronen-Rastermikroskopie und die Elektronenstrahl-Mikroanalyse

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US3714424A true US3714424A (en) 1973-01-30

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US (1) US3714424A (enExample)
CH (1) CH520332A (enExample)
DE (1) DE2011193C3 (enExample)
FR (1) FR2084337A5 (enExample)
GB (1) GB1293716A (enExample)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4277679A (en) * 1979-01-26 1981-07-07 Siemens Aktiengesellschaft Apparatus and method for contact-free potential measurements of an electronic composition
US4308457A (en) * 1979-05-25 1981-12-29 Ernst Leitz Wetzler Gmbh Device for the detection of back-scattered electrons from a sample in an electron microscope
US4554455A (en) * 1982-08-16 1985-11-19 Hitachi, Ltd. Potential analyzer
US4629889A (en) * 1983-06-24 1986-12-16 Hitachi, Ltd. Potential analyzer
US5412210A (en) * 1990-10-12 1995-05-02 Hitachi, Ltd. Scanning electron microscope and method for production of semiconductor device by using the same
US5594245A (en) * 1990-10-12 1997-01-14 Hitachi, Ltd. Scanning electron microscope and method for dimension measuring by using the same
EP0753200A4 (en) * 1993-07-30 1998-04-01 Electroscan Corp PERFECTED MICROSCOPE WITH ELECTRONIC SCANNING IN A PERFECTED NATURAL ENVIRONMENT
US5866904A (en) * 1990-10-12 1999-02-02 Hitachi, Ltd. Scanning electron microscope and method for dimension measuring by using the same
US6633034B1 (en) * 2000-05-04 2003-10-14 Applied Materials, Inc. Method and apparatus for imaging a specimen using low profile electron detector for charged particle beam imaging apparatus including electrostatic mirrors
WO2010148423A1 (en) * 2009-06-22 2010-12-29 The University Of Western Australia An imaging detector for a scanning charged particle microscope
US20150083912A1 (en) * 2013-03-25 2015-03-26 Hermes Microvision Inc. Charged Particle Beam Apparatus
US10236156B2 (en) 2015-03-25 2019-03-19 Hermes Microvision Inc. Apparatus of plural charged-particle beams
US11933668B2 (en) * 2020-02-03 2024-03-19 Rohde & Schwarz Gmbh & Co. Kg Sampling assembly and testing instrument

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8515250D0 (en) * 1985-06-17 1985-07-17 Texas Instruments Ltd Testing of integrated circuits
DE3602366A1 (de) * 1986-01-27 1987-07-30 Siemens Ag Verfahren und anordnung zum nachweis der auf einer probe von einem primaeren korpuskularstrahl ausgeloesten sekundaerkorpuskeln

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3535516A (en) * 1966-10-17 1970-10-20 Hitachi Ltd Electron microscope employing a modulated scanning beam and a phase sensitive detector to improve the signal to noise ratio

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3535516A (en) * 1966-10-17 1970-10-20 Hitachi Ltd Electron microscope employing a modulated scanning beam and a phase sensitive detector to improve the signal to noise ratio

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4277679A (en) * 1979-01-26 1981-07-07 Siemens Aktiengesellschaft Apparatus and method for contact-free potential measurements of an electronic composition
US4308457A (en) * 1979-05-25 1981-12-29 Ernst Leitz Wetzler Gmbh Device for the detection of back-scattered electrons from a sample in an electron microscope
US4554455A (en) * 1982-08-16 1985-11-19 Hitachi, Ltd. Potential analyzer
US4629889A (en) * 1983-06-24 1986-12-16 Hitachi, Ltd. Potential analyzer
US5969357A (en) * 1990-10-12 1999-10-19 Hitachi, Ltd. Scanning electron microscope and method for dimension measuring by using the same
US5412210A (en) * 1990-10-12 1995-05-02 Hitachi, Ltd. Scanning electron microscope and method for production of semiconductor device by using the same
US5594245A (en) * 1990-10-12 1997-01-14 Hitachi, Ltd. Scanning electron microscope and method for dimension measuring by using the same
US6114695A (en) * 1990-10-12 2000-09-05 Hitachi, Ltd. Scanning electron microscope and method for dimension measuring by using the same
US5866904A (en) * 1990-10-12 1999-02-02 Hitachi, Ltd. Scanning electron microscope and method for dimension measuring by using the same
EP0924743A1 (en) * 1993-07-30 1999-06-23 Philips Electronics North America Corporation Detector assembly for a scanning electron microscope
EP0753200A4 (en) * 1993-07-30 1998-04-01 Electroscan Corp PERFECTED MICROSCOPE WITH ELECTRONIC SCANNING IN A PERFECTED NATURAL ENVIRONMENT
US6633034B1 (en) * 2000-05-04 2003-10-14 Applied Materials, Inc. Method and apparatus for imaging a specimen using low profile electron detector for charged particle beam imaging apparatus including electrostatic mirrors
WO2010148423A1 (en) * 2009-06-22 2010-12-29 The University Of Western Australia An imaging detector for a scanning charged particle microscope
US20150083912A1 (en) * 2013-03-25 2015-03-26 Hermes Microvision Inc. Charged Particle Beam Apparatus
US10020164B2 (en) * 2013-03-25 2018-07-10 Hermes Microvision Inc. Charged particle beam apparatus
US10236156B2 (en) 2015-03-25 2019-03-19 Hermes Microvision Inc. Apparatus of plural charged-particle beams
US11217423B2 (en) 2015-03-25 2022-01-04 Asml Netherlands B.V. Apparatus of plural charged-particle beams
US11933668B2 (en) * 2020-02-03 2024-03-19 Rohde & Schwarz Gmbh & Co. Kg Sampling assembly and testing instrument

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Publication number Publication date
GB1293716A (en) 1972-10-25
DE2011193C3 (de) 1974-03-28
CH520332A (de) 1972-03-15
FR2084337A5 (enExample) 1971-12-17
DE2011193A1 (de) 1971-09-23
DE2011193B2 (de) 1973-08-23

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